1. Field of the Invention
The present invention relates to a process for the production of glycidyl nitrate. More particularly, the present invention relates to a scalable, continuous process for the production of glycidyl nitrate from glycerin, nitric acid and caustic.
2. State of the Art
It has been recognized that poly(glycidyl nitrate) is an excellent energetic polymer that may be used as an explosive agent, a propellant, or the like. However, conventional production of poly(glycidyl nitrate), or “PGN” for short, is complicated, may be dangerous, and is oftentimes expensive. The costs and danger involved in the production of PGN limit the use of PGN as a viable explosive agent or propellant.A process for producing improved PGN to be used as a binder in high-energy compositions such as propellants, explosives, gasifiers, and the like is disclosed in U.S. Pat. No. 5,120,827, issued to Willer et al. Willer et al. disclose that PGN may be formed by a combination of a reaction mixture, comprising a polyol initiator and an acid catalyst, with glycidyl nitrate (“glyn”): Addition of a glycidyl nitrate monomer to the reaction mixture at a rate essentially equivalent to on allows the formation of PGN to occur. A solvent, such as methylene chloride, ed to the reaction mixture with the glycidyl nitrate.
Unfortunately, production of PGN by the Willer et al. method is limited by the availability of glycidyl nitrate, which must be produced or procured to make PGN. Glycidyl nitrate is an expensive monomer and is not available commercially. In addition, purification methods used to prepare glycidyl nitrate are dangerous because they require distilling an unstable explosive. Furthermore, these purification methods are unable to produce glycidyl nitrate having a purity that may be used in the Willer et al. PGN production process.
For example, glycidyl nitrate may be produced in a multistep process by the nitration of epichlorohydrin with nitric acid, followed by the recyclization of the nitrated epichlorohydrin with a base to form glycidyl nitrate. During the cyclization step, however, an appreciable amount of epichlorohydrin is regenerated along with the glycidyl nitrate. The presence of epichlorohydrin with the glycidyl nitrate during polymerization to PGN reduces the energetic characteristics of the PGN and also undesirably chances the physical properties of the PGN. The presence of impurities of any kind is undesirable in the subsequent polymerization. Therefore, the epichlorohydrin must be distilled or otherwise removed from the glycidyl nitrate prior to polymerization. Additionally, glyn contains a thermally unstable oxirane ring that further sensitizes it toward deleterious thermal processes. This, in conjunction with the inherent instability of nitrate esters, makes the distillation process unsafe and expensive for large-scale production processes. Other methods of purification, such as chromatography or crystallization, also are not acceptable. Thus, the production of glycidyl nitrate from the nitratation of epichlorohydrin is a dangerous, inefficient, and expensive process for the production of glycidyl nitrate in large quantities using commercial-scale processing operations.
In another known process, distilled glycidol is treated with nitrogen pentoxide (N2O5) at a temperature of between −10° C. and −70° C. in an inert organic solvent such as dichloromethane (methylene chloride) to form glycidyl nitrate and nitric acid. To recover the glycidyl nitrate, the nitric acid is separated from the mixture. Millar et al. describe this process in U.S. Pat. No. 5,136,062. The production of glycidyl nitrate by the Millar et al. process is typically carried out in batch reactions at low temperatures. Millar et al. also describe a continuous mode of producing glycidyl nitrate, which is disclosed in U.S. Pat. No. 5,145,974. However, these processes do not lend themselves to the large-scale production of glycidyl nitrate because of the expenses involved and difficulty of employing the reagents in a commercial-scale production process. For instance, the glycidol used in this process must be procured as a specialty synthesis material and, as such, is expensive. In addition, glycidol can polymerize catastrophically above ambient temperature and, therefore, must be stored at reduced temperatures. Similarly, the use of nitrogen pentoxide is expensive because it must be prepared using specialized equipment and must be stored at cryogenic temperatures. Low temperature synthesis processes are costly due to the operating and equipment costs incurred to ensure that low temperatures are maintained for the synthesis reactions.
The processes currently available for producing glycidyl nitrate are not economically feasible for the large-scale commercial production of glycidyl nitrate are not economically feasible for the large-scale commercial production of glycidyl nitrate. Furthermore, the known methods of producing glycidyl nitrate are inherently dangerous. Therefore, a safe and relatively inexpensive process for producing glycidyl nitrate in large quantities is desirable. It would also be desirable to develop a commercial process for producing glycidyl nitrate having purity sufficient for use in a PGN process without the need for further distillation or reaction.